This invention relates to processes for preparing and using an ionographic imaging member, and in particular, to a process for forming a uniform dielectric imaging layer on a cylindrical substrate and forming images with the imaging member.
In electrography, an electrostatic latent image is formed on a dielectric imaging surface of an imaging layer (electroreceptor) by various techniques such as by an ion stream (ionography), stylus, shaped electrode, and the like. Development of the electrostatic latent image may be effected by contacting the imaging surface with electrostatically attractable marking particles whereby the marking particles deposit on the imaging surface in conformance to the latent image. The deposited marking particles may be transfered to a receiving member and the imaging surface may thereafter be cleaned and cycled through additional latent image forming, marking particle contact, marking particle transfer and cleaning steps. These imaging steps are well known in the art of electrography and disclosed in many patents, for example, in U.S. Pat. Nos. 4,410,584, 4,463,363 to Gundlach et al, 4,524,371 to Sheridan et al, 4,644,373 to Sheridan et al, and 4,584,592 to Tuan et al.
For high quality images, the dielectric layer should have a smooth imaging surface and uniform thickness. Variations in dielectric imaging layer thickness can cause variations in image density and resolution. Most prior techniques for fabricating electroreceptor or dielectric imaging layer thicknesses are expensive and difficult to carry out to produce layers having minimal variance in layer thickness. Although a dielectric sheet can be formed by extrusion and the resulting film laminated to a conductive substrate, the resulting seam is undesirable because high quality images cannot be formed on the seam and devices for cleaning of the electroceptor, e.g. blades, can be damaged by repeated collisions between the blade and the seam during cycling. Also, a dielectric sheet laminated to a conductive substrate may not make intimate electrical contact with the entire surface area of the substrate and the resulting air gaps and their associated dielectric properties are undersirable because high quality images cannot be formed in regions of varying dielectric thickness.
Seamless dielectric layers for electrophotographic imaging members have been prepared by spraying, both solution and powder spray with or without electrostatic enhancement. However, difficulties have been encountered with undesirable surface characteristics of layers formed by spray coating. For example, leveling of the spray deposited coating have often been uneven and orange peel effects have been observed. Moreover, disposal of solvents present handling, toxicity, and contamination difficulties. Moreover, maintenance of spray apparatus is complex and requires a special clean room to eliminate contaminants. Further, considerable material loss is encountered due to overspray. In addition, pin holes can form in the electroreceptor layer thereby adversely affecting image quality. Also, extended drying and or curing at times are necessary to achieve the final electroreceptor layer. Moreover, it is difficult to maintain uniform thickness throughout the electroreceptor layer. Spray coating of electroreceptor layers has also been undesirable or unsuitable where substrates are employed that are solvent or heat sensitive. For example, a temperature sensitive substrate cannot be employed where the electroreceptor comprises a thermoset resin which must be cured by heat. Moreover, multiple spray passes are required for depositing thick electroreceptor coatings. Multiple spray passes with either solution or powdered materials compound many of the above described difficulties and increase the expense and time to form the coatings. Also, the deposition of coatings by spraying results in the building up of the thickness at the edges of the coating which prevents the formation of quality images up to the coating edge.
Seamless dielectric layers for electrophotographic imaging members have also been prepared by dip coating. However, difficulties have been encountered with undesirable surface characteristics of layers formed by dip coating. For example, dip coated layers have often been uneven axially, show sagging, and orange peel effects have been observed. Further the thickness uniformity is adversely affected by variations of the speed of withdrawal from the solution tank. Thus the process requires expensive speed control equipment.
Also, seamless dielectric layers for electrophotographic imaging members have been prepared by metal anodization and polymer fill. However, this process is restricted to metal members with insulating oxides and requires electrochemical and vacuum processing.